If both the vents (there should be two of them) were closed off, your fuel tank would start collapsing, and with the shape of it, you'd probably see evidence of that (kinks at the corners, etc.)ok, so a jerry can made truck work great. Only scenerio i see, between the can and tank ARE not sharing, is the vent tube. Can the one off the tank, be pinched?
I will do this today. I checked all lines for kinks again last night, and everything looks fine.This is a good head scratcher.
Do you have a way to monitor voltage to the fuel pump while driving?
I had a fuel pump go bad, when I checked the voltage at idle (which the truck could barely hold) to the pump, it was 7.5VDC. Not good. . . .
It doesn't sound like a bad fuel pump, but if the internals are shorting out or causing a high current draw, voltage will decrease.So a pump that is going bad can have a low voltage?